I am having problems using an AJAX response.

Here is the JavaScript code:

2.  $.ajax({
3.     type: 'POST',
4.     url: ajaxurl,
5.     data: data,
6.     dataType: "JSON",
7.     success: function(r) {
8.         alert('Got this from the server: ' + r);
9. alert(r.description);
10.     }
11. });

The server uses json_encode, so the JSON is well-formed. Here is what I get from r.

1. Got this from the server: Array
   (
       [pid] => 1
       [uid] => 0
       [title] => 18
       [description] => 18
       [start] => 2010-06-13
       [end] => 2010-06-13
       [priority] => 1
       [complete] => 0
       [approved] => 1
   )
   {"id":"147","description":"18","title":"18","image":"today.png","completed":0}

But when I try to get the individual values such as r.description, it is undefined. What do I need to do to use the individual values?

Thanks,

John